Integral tank for transporting liquefied gas



A. GILLES 3,403,651

INTEGRAL TANK FOR TRANSPORTING LIQUEFIED GAS Oct. 1, 1968 3 Sheets-Sheet 1 Filed Feb. 14, 1966 I A. G\LLES 51M Inven+or Oct. 1, 1968 GILLES 3,403,651

. INTEGRAL TANK FOR TRANSPORTING LIQUEFIED GAS Filed Feb. 14, 1966 3 Sheets-Sheet 2 A. G \LLES JZNLfiwMFAQLM-s AH'omeys INTEGRAL TANK FOR TRANSPORTING LIQUEFIED GAS Filed Feb. 14, 1966 A. GILLES I Oct. 1, 1968 s Sheets-Sheet 5 Inverd-or il' MQY United States Patent 3,403,651 INTEGRAL TANK FOR TRANSPORTING LIQUEFIED GAS Auguste Gilles, Paris, France, assignor to Societe a Responsabilite Limittee dite: Gaz-Transport, Paris, France Filed Feb. 14, 1966, Ser. No. 527,263 Claims priority, application France, Mar. 5, 1965, 8,149 Claims. (Cl. 114-74) ABSTRACT OF THE DISCLOSURE A ship for carrying liquefied gases having inner and outer insulating containers between the hull of the ship and the tank. An elongated channel is carried by the containers and an elongated flange is continuously welded to an inner casing and having a hooked edge slidably mounted in the channel.

This invention relates to the maritime transport and to the storage while on land of liquefied gases, in particular liquefied natural gases having a high methane content. It is established practice to build tanks which are integrated into the structure of a ship in order to reduce the cost of thermally insulated tanks. This is done by lining the walls of the compartments of the ship with layers of fluid tight and heat insulating material, usually two in number. These layers are not in themselves rigid, and the hydrostatic pressures are sustained by the framework of the ship itself.

The principal difficulty encountered in the construction and use of these integrated tanks derives from the substantial contractions which result when the walls of the tank change from the ambient temperature to the boiling point of liquefied gas (160 C. in the case of methane). In order to avoid such contraction recourse is had to corrugations which extend in two directions at right angles to each other and require an excessive amount of metal. The metals used are ordinarily stainless steel or aluminum alloys, which are not brittle at low temperatures. Because of their complicated shape, it is difficult to support these metallic sheets throughout the range of temperatures to which they are subjected. The basic concept of the present invention, on the contrary, is to use a thin flat wall of Invar supported at all points by an insulating layer which is as rigid as possible. But then, for economic reasons, in view of the high price of these alloy steels, they are used in the form of very thin sheets (of the order of 0.5 mm. thick). The fluid-tight walls made of these sheets are in no way rigid, but are more like a skin, which transmits to the hull of the ship, through the thermal insulation, the hydrostatic pressures due to the weight of the liquefied gas, but may deform dangerously in the case of even a slight accidental depression in the tank which may occur while it is being, emptied. On the other hand, if this skin is fastened to the thermal insulation, the points by which it is attached may tear oiI during these contractions, which cannot be completely avoided, since the heat insulation does not ordinarily participate in these contractions.

The present invention seeks to avoid these difiiculties by providing connecting means which resists both traction and compression between each of the fluid-tight walls and the framework of the ship, so as to avoid any deformation perpendicular to the fluid-tight walls, and by permitting those walls to move longitudinally with respect to the thermal insulation.

The object of the present invention is to provide a new article of manufacture which consist of a fluid-tight, thermally insulated tank, integrated with the framework of the ship and comprising two fluid-tight walls and two heat insulating walls, one of the latter being positioned between the two fluid-tight walls. The tank is characterized by the fact that: p

1) One of the heat insulating walls comprises boxes filled with an insulating material and fastened directly to the inner hull or a transverse bulkhead in a ship by means of threaded metal pins welded thereto.

(2) One of the fluid-tight walls comprises thin plates of metal having a high nickel content and provided with inwardly projecting flanges, approximately as wide as the boxes are thick.

(3) These plates are welded along their flanged edges to the two opposed surfaces of one flange of an angle member, the other flange of which is seated so that it may slide longitudinally in a channel member fastened to the central part of each box.

(4) The outer heat insulating wall comprises boxes filled with a heat insulating material identical to that in the insulating wall previously described, in staggered relationship with respect to the boxes of said first mentioned heat insulating wall, so that the joints are out of registry.

(5) These boxes are fastened by means of screws to a series of vertical metallic shapes positioned between the vertical stacks of boxes.

(6) The shapes are themselves supported by supporting members which extend through one of the fluid-tight walls, without impairing its impermeability, on rods which are slidably mounted from place to place along horizontal wooden bulwarks, which are themselves supported and attached from place to place to brackets welded to the inner hull.

(7) The bulwarks are in several sections each free to expand longitudinally. Finally, the other fluid-tight wall comprises thin plates made of steel having a high nickel content and flanges substantially as wide as the boxes are deep. This width is dependent on the accidental depression which may occur when the tank is being emptied. The plates are welded to two of the flanges of a channel member which is so hooked onto a similar channel member fastened to one of the edges of each of the boxes, that the first mentioned channel member may slide longitudinally with respect to the second.

In order that the invention may be more clearly understood, one embodiment thereof will now be described, purely by way of example, in conjunction with the accompanying drawings, in which:

FIG. 1 is a vertical section taken through one part of the tank, but without showing any of the boxes as cut;

FIG. 2 is a horizontal section taken through one part of the tank, but without showing any of the boxes as cut;

FIG. 3 is a detail view showing on an enlarged scale the part III of FIG. 1;

FIG. 4 is a detail view showing on an enlarged scale the part IV of FIG. 1;

FIG. 5 is a top view, showing on an enlarged scale the joint between the components of the horizontal bulwark;

FIG. 6 is a detail view showing on an enlarged scale the part VI of FIG. 1;

FIG. 7 is a vertical section on a larger scale showing the attachment of the vertical shapes; and

FIG. 8 is a corresponding horizontal section with part of the tank removed.

The tank is built within a ship having an outer hull, inner hull and a supporting framework between the hulls so as to leave the inner surface of the inner hull substantially clear and smooth. For the sake of stability and convenience in construction, the inner hull may have approximately the same general shape as the outer hull, but be more polygonal, usually octagonal, that is to say, like a rectangle with 4 bevelled corners. The ship also comprises, from bow to stern, a series of compartments for holding liquefied gas, separated from each other by transverse bulkheads comprising two parallel walls spaced by the necessary supporting framework.

Inside each of these compartments is an integral tank comprising two fluid-tight casings alternating with two heat-insulating casings.

The outer heat insulating casing is constructed by covering the inner surface of the inner hull with boxes 1 which have the shape of a parallelepiped, may be made of wood, for example, and contain a heat insulating material, preferably Perlite. These boxes are provided, on each of their small vertical end faces, with a bracket 2 by means of which they may be fastened to the inner hull 3 or the bulkhead 4 by means of threaded studs 5 welded direct to the inner hull as shown on FIG. 3. A large washer 6 held by a nut 7 makes it possible to fasten two adjacent boxes 1 to the inner bull, or even four, if the studs are positioned at the corners.

The outer fluid-tight casing comprises a series of plates 8 of thin sheet metal, 0.5 mm. thick, made of a metal having a high nickel content so as to have a very low coefficient of heat expansion without being brittle at low temperatures. The metal sold under the trademark Invar is most suitable. These plates are plain strips, very flexible because so thin, and provided with two flanges 9 which project perpendicularly inward, as shown in the drawings.

A mounting member 10 consisting of a bracket having a horizontally positioned flange is stapled to the middle of each box 1. This bracket is preferably made of the same metal and of the same thickness as the plates.

The plates 8 are positioned as shown in FIG. 1 between two successive brackets 10. Each of the flanges 11 of these brackets contacts on each face an edge 9 of one of two successive plates. The assembly comprises three layers of metal which may be suitably welded together along a continuous seam by an electrical welding machine, or by fusing the edges together without adding any metal, so as to maintain the impermeability of the outer fluid-tight casing and fasten it to the boxes 1, and thus to the inner hull 3.

For all these casing walls, especially those extending longitudinally of the ship, i.e., the floor, ceiling and lateral walls of the tank, it is preferable to use mounting means 10 comprising two parts, one of which has an L-shaped section formed by the perpendicular flange 11 and another flange parallel to the wall of the tank. This last flange is seated in a channel 12 as shown in FIG. 4, and the channel member itself is fastened to the wall of the box 1 by means of staples 13. In this way, the outer fluid-tight casing is firmly supported by the boxes 1, and thus by the inner hull 3, against stresses perpendicular to the brackets 10 (and either perpendicular to the wall or parallel thereto) but are movable with respect to the boxes in response to longitudinal stresses, which arise especially when the ship is flexed by wave action.

The inner heat-insulating casing comprises boxes 14 similar to boxes 1, which are positioned athwart the joints between the boxes 1 in both directions, the boxes 14 being positioned vertically between the brackets 10 and the welded edges 9 of the plates 8. The boxes may not, however, be attached at this point to the plates 8, since they are not strong enough.

The boxes are therefore fastened to a series of bulwarks 15 parallel to the axis of the ship and spaced about the hull. These bulwarks are supported from place to place by iron brackets 16 having an end flange 17, as shown on FIGS. 1 and 5. The bulwarks 15 are made up of several sections having beveled ends connected as shown in FIG. 5, with each connection resting on a bracket 16. One of the bulwarks illustrated is fastened to each of the brackets 16 by means of one or more screws 18 which pass through the flange 17, while the other bulwark is simply held by a U-shaped hook 19, which permits some free play in a longitudinal direction,

to compensate for changes in its length resulting from contraction or hygrometric causes. Naturally, in each row of brackets 16 and bulwark sections 15 each bulwark section is fixed at one end and free at the other.

A rectangular hanger 20 is mounted on each of the bulwarks 15 and fixed to a plate 21 in which a cylindrical stud 22 is welded, as shown in FIGS. 7 and 8. This stud passes through a large hole 23 in the outer fluid-tight casing 8, and is sealed to that casing by a large disk 24 and a small disc 25. A support 27 having the shape shown in FIGS. 7 and 8 and comprising a cylindrical vertical portion 28 is held on said stud by the nut 26.

Naturally, while the tank is being built, the bulwarks 15 and hangers 20 are placed in position first, followed by the plates 8 above the boxes 1. This can be done easily because the openings 23 through which the studs pass are so large that no exactitude is required. A disk 24, a little thicker than the plates 8, is then placed over each of the openings 23 and welded to the periphery thereof. Finally, the disk 25, which automatically centers itself on the stud 22 is added. This disk 25, which is thicker than the disk 24, is welded thereto and to the stud 22, and holds the entire casing wall against the boxes by means of a device not shown which is held in place by the stud. It only remains to mount the assembly comprising supports 27, which may be prefabricated, by purely mechanical means.

Vertical channel members 29 may then be mounted on the supports 27, as shown in FIGS. 1, 2, 7 and 8, so as to extend from one row of bulwarks to the next, and comprise at each end a transverse wall 30 pierced by a circular orifice 31. As shown best in FIG. 7, the cylindrical portion 28 of each of the supports 27 extends further past the bottom of that support than past the top. This makes it possible to mount the vertical channel members 29 very easily by first fitting their upper opening 31 onto the lower part of the cylindrical part 28, and then raising the channel member to seat the lower orifice 31 on the upper portion of the cylindrical part 28 of the lower supporting member. The section of channel member 29 thus slightly overlaps the member 28 at one end, without being liable to come loose at the other, and may be fastened in place, for safetys sake, by simply inserting a pin in a hole 32 provided for this purpose. In this way it is easy to mount the members 29, and they are free to expand and contract, yet it is not necessary that they be manufactured to any exact tolerances.

The insulating boxes 14 of the inner heat insulating casing may then be simply attached by means of screws 33 which screw into one of the flanges of the channel member 29 or into a nut 34 welded thereto. These screws, like the screws 7 for the outer casing, bear through a large washer 35 on abutments 36 nailed to the small vertical end surfaces of the boxes 14.

It will be seen that when screws 33 are tightened, the boxes 14 are rigidly fastened to the inner hull 3 by the channel members 29, the supports 27, the studs 22, the hangers 20, the bulwarks 15 and finally the brackets 16 welded to said hull. This manner of attachment does not, however, provide a path which conducts heat because of the presence of the bulwarks and the length of the path. On the other hand. the impermeability of the outer fluidtight tank is not impaired because of the seal around the studs 22.

FIG. 2 also shows that this arrangement makes it possible to stagger the vertical joints between the boxes 1 and 14 to avoid the superposition of any joints whether horizontal or vertical. Naturally, any open spaces of any size are filled with boxes of approximate sizes for the ends, or by means of pieces of expanded plastic material cut to suit, as for instance in the case of the spaces between two boxes 1 in FIG. 3 or in the corners between two walls.

Finally, the inner heat insulating casing having thus been rigidly fastened in place, the inner fluid tight casing is fastened thereto. The inner fluid-tight casing comprises, just like the outer fluid-tight casing, a plurality of plates 37 of the same size as those in the outer casing and provided with the same flanges. This dimension of the plates 37 is determined by their thickness so that they are capable of resisting the maximum subatmospheric pressure which may accidentally be created in the tank while it is being emptied. This sub-atmospheric pressure is limited by safety means to a small differential of the order of 30 millibars. This leads to a flange width of about 400 mm. when the plates are 0.5 mm. thick. However, in the case of the inner fluid-tight casing the mounting means 38, instead of being positioned like members at the middle of the boxes 1, are preferably positioned along one edge thereof, preferably the upper edge. This makes it possible to replace the plain corner member with a rectangular plate, which is stapled parallel to the wall 37, which imparts to it a greater resistance to sub-atmospheric pressures.

In like manner the mounting means 38 associated with the walls parallel to the longitudinal axis of the ship may be replaced by two interlocked channel members as shown on FIG. 6, one of said interlocked members comprising a horizontal flange 39 to which the two edges 40 of the plates 37 are welded, while the other like the member 12, is fastened by means of staples 42 to that wall of the box 14 which is perpendicular to the plate.

In this case as well the fluid-tight casing and boxes 14 may move longitudinally with respect to each other, while transferring perpendicularly to the member 38 those forces which act parallel or perpendicular to the wall 37. However, in the present case, the resistance to traction in a direction perpendicular to the wall is much greater than in the case of FIG. 4, which is quite important, since while the tank is being emptied, the inner fluid-tight tank may be subjected to sub-atmospheric pressure, whereas the outer fluid-tight casing is always subjected to the same pressure on both sides because the two heat insulating casings on opposite sides thereof are kept in contact with the upper part of the ship.

It will be appreciated that the embodiment which has just been described has been given purely by way of example and may be modified as to detail without thereby departing from the basic principles of the invention. In particular the height of the plates 8 may be a multiple of that of the plates 37 since the outer fluid tight-casing is not subjected to low pressures.

What is claimed is:

1. In combination with the hull of a ship, the improved tank for holding liquefied gas which comprises an outer layer of heat insulation fastened directly to the hull of the ship, an outer fluid-tight casing, supporting means made of a material which is a poor conductor of heat between said outer fluid-tight casing and hull, carried by said hull, and carrying said outer fluid-tight casing, an inner layer of heat insulating material comprising a plurality of insulation-holding containers, means sealingly extending through said outer fluid-tight casing which fasten said inner layer of heat insulating material to said supporting means, an inner fluid-tight casing, elongated channel means carried by said containers, said channel means being closed on the side facing toward said inner casing, and an elongated flange continuously welded to said inner casing and having a hooked edge slidably seated in said channel means to prevent movement of said inner casing away from said containers while permitting relative movement between said casing and containers in a direction parallel to said inner casing.

2. A tank as claimed in claim 1 in which the walls of said outer fluid tight casing are fastened to said support means by means permitting relative sliding between said outer fluid tight casing and support means in a direction parallel to said fastened wall.

3. A tank as claimed in claim 1 in which said fluid tight casings are formed from plates of metal less than 1 mm. thick having a low coefficient of heat expansion and provided with transverse peripheral flanges for increasing their resistance to deformation, and said elongated flanges have an edge continuously welded between the peripheral flanges of adjacent plates.

4. A tank as claimed in claim 1 in which both of said heat-insulating layers are formed from rows of insulation holding containers, the edges of the containers of one layer being staggered with respect to the edges of the containers of the other layer.

5. A tank as claimed in claim 1 in which said supports are made in sections, one end of each section being fixed to said hull, while the other is slidably attached thereto.

6. A tank for holding liquefied gas comprising successively an outer wall, an outer insulating layer fixed to said outer wall, insulating support means fixed to said outer wall and extending through said outer insulating layer, an outer fluid-tight casing mounted on said insulating support means for sliding movement relative thereto in a direction parallel to said outer wall, an inner insulating layer comprising a plurality of insulation holding containers supported by said insulating support means, an inner fluid-tight casing, elongated channel means carried by said containers, said channel means being closed on the side facing the said inner casing, and an elongated flange continuously welded to said inner casing and having a hooked edge slidably seated in said channel means to prevent movement of said inner casing away from said containers while permitting movement between said inner casing and containers in a direction parallel to said inner casing.

7. A tank as claimed in claim 6 in which said fluidtight casings are formed from plates of metal less than 1 mm. thick having a low coeflicient of heat expansion and provided with transverse peripheral flanges for increasing their resistance to deformation.

8. A tank as claimed in claim 6 in which both of said heat-insulating layers are formed from rows of insulation holding containers, the edges of the containers of one layer, being staggered with respect to the edges of the containers of the other layer.

9. A tank as claimed in claim 7 in which said channel means are positioned beneath the inner surface of the containers so that said inner casing lies flush against said inner container surfaces.

10. A tank for holding liquefied gas comprising an insulating wall formed from a plurality of insulation holding containers, and a fluid-tight casing supported against the inside of said insulating wall, said casing being formed from a plurality of rows of metal plates less than 1 mm. thick, having a low coeflicient of heat expansion, and provided with transverse peripheral flanges, elongated channel means carried by said containers, said channel eans being closed on the side facing said casing, and an elongated flange continuously welded to said casing between the flanges of adjacent rows and having a hooked edge slidably seated in said channel means to prevent movement of said casing away from said containers while permitting relative movement between said casing and containers in a direction parallel to the inner surface of said containers.

References Cited 

